The present invention relates to a striated belt and, more particularly, to a V-profiled belt intended for automotive applications.
The Applicant markets striated belts with V-shaped teeth, the so-called adapted-modulus belts, said belts comprising polyamide 6.6 twisted strands and being intended for electric household appliances, such as linen washers and dryers.
Such belts have a stress-elongation diagram, which characterizes their modulus of elasticity and the average slope of which, between 1% and 10% of elongation, is substantially equal to 5.5 daN/% of elongation, per belt width centimeter and per strand.
Said belts are mounted, with a fixed distance between axes, by tensioning them and, once positioned, by releasing them (the so-called automatic mounting process or xe2x80x9csnap-onxe2x80x9d)
Anyway, belts of this type but usable for automotive applications are not on the market at the present time.
As a matter of fact, the use of twisted strands in a striated belt intended for automotive applications, so as to transmit power between an engine and a receiving device, such as an alternator, means a number of problems, especially owing to the acyclic property of the engine output curve, said acyclic feature being sharper for four-cylinder engines than for six- or eight-cylinder engines and being quite greater in diesel engines than in gasoline engines.
Since the electrical power requirements of automotive vehicles tend to increase at present (air conditioning, etc.), the amperage of alternators has to be increased too, and therefore their inertia, which increases proportionately the stresses imposed upon the
Accordingly, it is an object of the present invention to provide a belt for a motor vehicle, which exhibits a long service life even under high loads.
It is another object of the present invention to provide a belt capable of operating with engines having a marked acyclic feature.
It is still another object of the present invention to provide a belt for a motor vehicle, allowing the filtering out of the high-order harmonic components of the speed and voltage signal output by the receiving device, more particularly when the latter is an alternator.
It is another object of the present invention to provide a belt capable of being incorporated in a drive system between a driving shaft and a driven shaft, by means of an automatic mounting operation (xe2x80x9csnap-onxe2x80x9d), advantageously without requiring a fixed tightener.
To achieve at least some of the above objects, there is provided a power transmission striated belt which includes an elastomeric matrix and a lengthwise supporting structure consisting of polyamide 4.6 twisted strands, characterized in that the supporting structure is selected so that the stress-elongation diagram of the belt exhibits an average slope ranging from 12 to 20 daN/% of elongation per width centimeter and per strand, and in that the twisted strands are wound with a very small nominal tension, or almost without any tension, and in that the curing operation and the cooling operation after curing are carried out without any belt tensioning. More particularly, said average slope may range from 12 to 15 daN/% of elongation per width centimeter and per strand.
It should be noted that the Patent Application U.S. Pat. No. 4,701,377 and the European Patent Application EP-381 281 relate to a striated belt, in which the high elastic modulus twisted strands are made of polyamide 4.6, but said documents do not suggest using such twisted strands for a low-modulus belt.
As a matter of fact, it should be observed that the average slope of the useful domain of the elongation curve is in the order of 30 daN/% of elongation per width centimeter and per strand for the motor vehicle belts known at present. Besides, the ultimate elongation of such belts is generally below 10%.
According to the present invention, said average slope, between 1% and 10% of elongation, is preferably substantially equal to 17 daN/% of elongation per width centimeter and per strand.
The belt is advantageously characterized in that its length, as measured on a test bench according to the ISO Standard 9981, is lower by 1%-6% and, for instance, by 1%-5% or by 1%-4%, than the nominal length of said drive system.
In a preferred embodiment, the length of said belt, as measured on a test bench, is lower by 2%-3% than the nominal length of said drive system, the preferred value being substantially equal to 2%.
Advantageously, the belt has a stable operating tension ranging from 14 to 20 daN/width centimeter/strand and, more preferably, ranging from 14 to 17 daN/width centimeter/strand.
The twisted strands of the belt have a diameter d preferably ranging from 0.7 to 1.3 mm.
The space between twisted strands ranges advantageously from 0 (close-turn lay) to 4 d, and preferably from 0 to 2 d.
The invention also relates to a manufacturing method for the above-mentioned belt, characterized by the following steps:
a) forming, for instance on a drum, a belt blank, such step including the helical winding of twisted strands at a nominal tension either very low or almost null;
b) curing the blank without subjecting it to any mechanical tensioning;
c) allowing the cured blank to cool down without subjecting it to any mechanical tensioning;
d) cutting the cured blank into individual belts.
The invention also relates to a method of the so-called xe2x80x9cautomaticxe2x80x9d type for mounting the belt onto a pulley of a drive system. It is characterized by the following steps:
i) positioning a mounting tool close to the pulley, so that at least a radial thrust area of the mounting tool rests against the pulley girth, the mounting tool including a ramp area extending from the groove of the pulley to a downward area, for the guidance of the belt right from the groove while keeping it away from the pulley till it reaches a plane spaced from said pulley face;
ii) radially moving said mounting tool by a lever effect, while following the pulley girth so as to fit the belt into the groove of the pulley while pulling on it;
iii) once the belt is positioned in the groove, disengaging the mounting tool.
Last, the present invention relates to a drive system between a pulley integral with a driving shaft of a car engine and at least one pulley integral with a driven shaft of a receiving device, such system comprising a belt as defined above and without any fixed tighteners.